Blackface/Whiteface

Upon looking at this old image of Al Jolson - many people become upset, while others dismiss it as a vestige from a bygone era.
But what is so offensive about some burnt cork spread across one's face?

Gul Tuysuy (on a Turkish news show) seems to think that when speaking about the Black POTUS - it's okay to wear blackface to emphasize... what?

That he agrees or disagrees with Obama's policies?

That Obama is Black?

That he is stereotypically Black?

Or that he still harbours some hostility for the Muslims renaming Constantinople... Istanbul?

But who, that is white, can wear blackface and get away with it?

Is it okay for an actor who is playing an actor who is from another country?

Or if it is an actor in a movie with Richard Pryor, in an earlier stage of our racial consciousness, who wears the cork to save his characters life?

But not if an actor dons the stuff to fit through a loophole to benefit his character chances at a better education?

Or is it okay if your hittin' Whoopi Goldberg and the joke is on her?

Even Dave Chapelle wore whiteface (although an actual photo is hard to get).

Eddie Murphy played a white guy on several occasions.

Are the Wayans "Racist" for mocking the silliness of white heiresses?

Is the Zulu Crewe acting coonish when they wear blackface during their Mardi Gras parades in NOLA?

According to one source;

http://www.jackherer.com/chapter13.html

the laws that established blackface in the Jim Crow laws were first created in NOLA to prevent marijuana smoking Blacks from thinking that they were equal to whites.

So, what are the rules when wearing makeup to look like another race?

As long as the joke/skit/performance is funny?

As long as one is not mocking or degrading another race?

As long as you're not white?

As long as you're not Black?

As long as the makeup has some context to what you are referring?

Am I offended by Mr. Tuysuy's blackface?

Nope. I'm more dismissive of him as being simple. In fact, seeing the image, I have no interest in what he has to say.

So the bottom line is - what was his point?